It is variously estimated that in the United States alone there are 110 to 132 million wood poles in active use by utility companies and systems. Of these it is further estimated that there are 20 to 30 million standing poles in the field which need replacement now with another 4 to 6 million being added each year.
The problem, of course, is that wood rots. Untreated wood in the presence of adequate oxygen and moisture is attacked by fungi. There are other reasons for causing a pole to be classified as defective, however. Besides the various forms of mechanical damage, woodpeckers make hollows for nests, and carpenter ants, buprestid beetles and termites find poles desirable as living quarters and food.
Those skilled in the art such as owners of utility poles, posts, poles and railroad support pilings are well aware of the decay to which poles are subject. This is particularly true in the groundline zone to a depth of about eighteen inches below and above the groundline level. Owners are generally agreed that poles which are to be replaced, for instance, or reset may require special protection against decay if they have been in place 6 or more years.
As mentioned above, in the presence of oxygen, moisture and temperature wood is attacked by various fungi which feed on or dissolve the cellulose and lignins in the wood. Thus, food is provided for further fungi development and growth, and this is true whether the pole is being relocated or whether it remains in place.
Groundline wood preservative treatments are intended to enhance the original preservative treatment by impregnating the outer circumferential area or shell to a depth of up to 2 inches with a preservative which will deny a food source for the fungi. Because of the enormous number of poles in service, even small per-unit savings achieved by delaying or avoiding pole replacement can extrapolate to huge savings.
The American Wood Preservative Association (AWPA) sets standards for wood preservative solutions by specifying, for instance, that the copper naphthenate solution shall be prepared with a solvent conforming to AWPA Standard P9 and which solution shall contain a minimum of 2 percent copper metal. However, none of the known treatments can produce 100% penetration of the wood. Accordingly, once a pole is set it is most important to protect the outer shell of the pole up to 2 inches in depth from deterioration because the shell represents 90% of the pole's strength. Poles which upon inspection reveal decay in the outer shell at or below groundline can be treated with preservatives applied to the surface of the pole through the vital zone. The ideal preservative is one which will fortify or restore the original preservative treatment by penetrating up to 2 inches of the wood.
There are several commonly employed or typical treatments for achieving the desired results. One consists of a groundline paste compounded of wood preservative and petroleum creosote material which acts as a carrier for the wood preservative. Once the ground has been removed from contact with the pole or post down to a depth of 20 to 24 inches, the surface of the pole is brushed clean of decayed wood and dirt. The paste mixture is liberally applied to or smeared on the pole from the groundline down to about 20 inches and then a protective wrap of kraft or roofing paper is applied to protect the paste from being absorbed into the surrounding soil. In all instances, the products used consist of various types of sodium fluoride, pentachlorophenol, pentachlorophenates, coal tar creosotes or petroleum greases. Several companies in the industry use the system just described.
Another method of treating a pole at groundline involves the use of a bandage or wrapper which consists of a kraft paper backing on which is spread the wood preservative and creosote paste mixture. Over the paste mix is disposed a protective plastic film. The purpose of the kraft paper is to furnish a stiffening effect for easy handling and application of the wrap. The plastic film is removed before the wrap is applied to a pole. An alternative is a fiber sheet in roll form impregnated with the wood preservative. The exact size wrap needed for a given pole is cut off the roll and tacked to the crucial zone of the pole.
Under EPA regulations some wood preservatives such as pentachlorophenol are classified as carcinogenics and are therefore subject restrictions in their applications.
There are a number of disadvantages in the known and currently used art. For instance, the amount of wood preservative which is carried in the paste mixture is limited. The use of known carcinogenic chemicals like pentachlorophenol and creosote are a danger not only to the soil environment around the pole but are also dangerous to the individual applying the system. Pentachlorophenol especially migrates in all directions so it will penetrate the pole but will also be absorbed into the surrounding soil.
In the known groundline treatment systems the encapsulating or carrier agent represents about 70% of the total weight of the wrap. The carrier agent, however, performs only a nominal function once the wood preservative is released.
The only prior art reference of which applicants are aware is U.S. Pat. No. 3,467,490. This patent is an example of a system which uses an encapsulating agent and thus is not particularly pertinent to the details of the invention described and claimed herein.